Method of recovering tin in the form of tin sulfide from a lowgrade unreduced tin ore



Patented Feb. 12, 1952 UNl'l'E STATS ATENT GFFICE METHOD F RECOVERING TIN IN THE FORM OF TIN SULFIDE FROM A LOW- GRADE UNREDUCED TIN ORE No Drawing. Application May 17, 1946, Serial No. 670,548

This invention relates to improvements inthe process of recovering tin in the form of tin sulfide from tin ores and other tin-containin materials in an unreduced state. In particular, it relates to the recovery of tin from unreduced low grade tin res and similar tin-bearing materials which contain relatively large amounts content of the material undergoing treatment it takes place.

In one such process, over which the present process is, in particular, an improvement, the tin ore is heated to a temperature of about 950 C. to 1100 0., in the presence of a relatively small amount of a solid carbonaceous reducing agent, at the most the amount theoretically required to reduce the tin content to a metallic state and produce carbon monoxide, and a sulfur compound. tinued at the said temperature until conversion of the tin and volatilization of the resulting tin sulfide is effected. Fusion of the ore generally takes place in such prior art process at the aforesaid sulfidizing and vclatilization temperatures, with the result that a substantial portion of the tin content becomes alloyed and, from economic considerations, lost. in consequence there is a substantial impairment of the yields of theoretically recoverable tin in such processes, particularly where the starting material is a low grade ore containing to and more of tin, and for such reason these processes have not met with commercial success.

We have found that fusion of the relatively high tin content ore undergoing treatment in accordance with the present invention can be prevented or minimized to a substantially inccnsequential extent by eiieoting sulfidization of the ore at temperatures of 950" C. to 1100 0., in the presence of relatively large. amounts of a solid carbonaceous reducing agent, at least about twice the tin-reducing equivalent of solid carbonaceous reducing agent, i. e., at least about twice the amount theoretically required to reduce The heating of the mixture is con- 2 Claims. (Cl. 23--136),

2 the tin. content to a metallic "state and produce carbon monoxide. Due to the use of such relatively large amounts of solid carbonaceous reducing agents, the tin content of the ore is relatively quickly made more amenable for reaction with a sulfidizing agent. In consequence there is a greater yield of theoretically recoverable tin than in the prior art processes referred to above, and these yields are obtained in substantially less time than heretofore.

The process of the present invention is effective for the treatment of all tin ores to recover the tin in the form of tin sulfide therefrom, but it finds its greatest efiectiveness for the treatment of comparatively low grade ore concentratescontaining from about 10% to 40% of tin and which have not been capable of commercial treatment prior to the present invention. Such concentrates often contain 5% or more of iron, in addition to substantial amounts of other impurities including silica, arsenic, antimony and sulfur. If sulfur is present in excessive amounts it may be desirable to roast the ore prior to treatment to recover tin to remove at least a portion thereof; however, this is not essential.

In carrying out the present invention to recover tin in the form of tin sulfide from a tin ore, the ore is pulverized to a finely divided state, for example, minus 20 to mesh, preferably minus or 200 mesh. The ground ore is then mixed with a solid carbonaceous reducing agent and a sulfidizing agent in powdered state, preferably of a mesh corresponding to the mesh of the ore to insure substantial homogeneity during mixing. If desired, the ore, solid carbcnaceous reducing agent and sulfidizing agent may be preliminarily mixed and. then ground to the desired fine particle size. The substantially uniform mixture of particles is then heated to a temperature in the order of about 950 C; to 1100" C. to substantially simultaneously reduce the tin and convert the same to a sulfide and to volatilize the resulting sulfide from the ore undergoing treatment.

The combined reduction and suliidizing reactions may be carried out in any suitable vessel such as a direct-fired rotary kiln, a multiple hearth or a Wedge type furnace, for example, either in a neutral atmosphere or a reducing atmosphere, preferably the latter. Oxidizing atmospheres should be avoided because such atmospheres induce oxidation of the tin and other metals in the ore and thereby cut down the yields of recoverable tin and add to the cost of the process.

As stated, the temperature at which the tin ore is reduced and sulfidized and the resulting tin sulfide volatilized therefrom may vary from about 950 C. to 1100 C., the preferred temperatures varying from about 1020 C. to 1060 C. The time of treatment of the ore may vary widely, from about 15 minutes upwardly. Usually the maximum amount of tin is reduced, sulfidized and volatilized in the form of tin sulfide in about one-half to one hour, although at times it is essential to prolong the reaction to somewhat above one hour in order to reduce and volatilize the maximum amount of tin out of the ore. Generally, reaction times in excess of about one hour are ineffective to increase to any substantial extent the amount of tin which can be reduced and volatilized from the ore in the form of tin sulfid in accordance with our process.

There is no exact temperature which may be utilized for optimum results in the reducing and sulfidizing treatments of the present invention, for the results are to some extent dependent upon the nature of the ore subjected to treatment. Thus, some Bolivian ores, in the absence of the relatively large amounts of solid carbonaceous reducing agent used in accordance with the present invention, fuse or melt to a very serious extent at a temperature of about 870 C. On the other hand, other Bolivian ores and many Mexican ores, similarly free from solid carbonaceous reducing agent, may be subjected to temperatures as high as about 980 C. or 1040 C. without encountering serious fusion. Since fusion of the ore must be avoided, it is manifest that the optimum temperature may be a little higher for one or than for another. Slight amounts of fusion resulting in some sintering of'the ore undergoing treatment may be tolerated in most cases. On the other hand, fusion to an extent such that pools of molten material are formed is detrimental and should be avoided. In general, satisfactory results are usually obtained with the relatively large amounts of solid reducing agents in accordance with the present invention within a temperature range of about 950 C. to 1060 C., and for most tin ores a temperature of from about 1020 C. to 1060 C. is most effective.

Generally, the amount of coal, coke, charcoal, peat or other solid carbonaceous reducing agent to beused should be at least about twice the amount theoretically required to reduce the tin content of the ore to a metallic state and produce carbon monoxide. In commercial scale operations, using a low grade ore containing from about to 40% of tin, at least about by weight of solid carbonaceous reducing agent, based on the weight of the ore, should be used. It is preferred, however, that the minimum amount of reducing agent used be about by weight and that the maximum be in the order of about 40% to 45%, since substantially larger amounts tend to coke. Solid carbonaceous reducing agents containing both nonvolatile and volatile reducing constituents, such as anthracite and bituminous coal, are preferred; the latter in particular because of its relative cheapness and availability.

Any sulfur-containing material, solid, liquid or gas, capable of reacting with tin at a temperature of from about 950 C. to 1100 C. to form a tin sulfide may be used in accordance with the present invention. The amount of sulfidizing agent which may be used may vary widely, from about 10% to 100% or even more, based on the weight of the tin-containing material being treated, in the case of sulfur. Equivalent amounts of other sulfur-containing materials such as ferrous sulfide, sulfur dioxide, sulfur-containing petroleum crudes, etc., may be used. Sulfur, however, is preferred because more of the tin is sulfidized and in less time than with the other sulfidizing agents. Optimum results are usually obtained with a low grade tin ore containing from about 15 to 35% of tin by using from about 25% to 50% of sulfur, based on the weight of the ore.

The exact nature of the reactions in the materials undergoing treatment is not known, although it is possible that the tin in the ore is reduced to a finely divided metallic state, the particles being separated by the excess coal and by other materials in the reduced ore, and the tin then reacts with the sulfidizing agent to form tin sulfide. Regardless of the mechanism of the reactions, the process is more effective than the prior art processes referred to above, involving the use of relatively small amounts of solid reducing agents in the sulfidizing reaction.

The following example is illustrative of a preferred embodiment of the present invention.

Ore containing about 21% tin, 22% iron, 19% silica, 2% sulfur, and other impurities in minor amounts was roasted in an oil-fired rotary furnace in an oxidizing atmosphere at a temperature of about 815 C. The roasted ore, which contained about 0.7% sulfur, was ball-milled to a particle size passing a 100-mesh screen. 100 parts by weight of the milled ore was intimately mixed with 40 parts of powered bituminous coal and 50 parts of powdered sulfur. The mixture was placed in a vessel and the latter was heated for 60 minutes at a temperature of 1060 C., in a non-oxidizing atmosphere of nitrogen. Under these conditions approximately of the tin content of the ore was volatilized in the form of tin sulfide.

In a similar experiment with the same tin ore-sulfur-coal charge at a temperature of 1100 C. for 30 minutes, approximately 89% of the tin content was volatilized from the ore. In another experiment similar to the illustrative example but with the tin ore in an unroasted state, approximately 95% of the tin content was volatilized from the ore. Lesser amounts of tin were volatilized from the ore when with the same tin ore lower temperatures and/or smaller amounts of coal were used.

It is manifest that the details as to time and temperature of reduction and sulfidization of the tin ore may be varied, as may also the proportions of coal and sulfur to ore, all as hereinabove set forth. It is also manifest that other sulfidizing agents such as ferrous sulfide, etc. may be used, although not with the especially desirable results obtained with sulfur. In an experiment similar to the illustrative example, using parts of the same roasted ore, 100 parts by weight of ferrous sulfide and 40 parts by weight of coal, and a heating time of 60 minutes at 1100 C., approximately 85% of the tin content was volatilized from the ore.

The recovery of the tin from the tin sulfide forms no part of our invention. Any of the conventional methods may be used for this purpose, such as those referred to in the British Patent No. 361,402, accepted November 18, 1931, for example.

In our copending application Serial No. 670,547, filed on even date herewith, now Patent No.

2,570,473, there is disclosed and claimed a process of recovering tin in the form of tin sulfide from a tin-containing ore, in which process the ore is preliminarily reduced under conditions such that the reduced ore contains tin in dispersed small particles in a form soluble in an aqueous-alkali solution at a temperature of at least about 75 C. to 90 C., and the reduced ore containing the said solubilized tin is then heated with a sulfidizing agent at a temperature sufliciently high to form tin sulfide and for a time sufiicient to volatilize the same from the ore undergoing treatment but below that at which the ore fuses.

We claim:

1. .In the method of recovering tin in the form of tin sulfide from a low grade, unreduced tin ore containing a substantial. amount of metallic impurities and about to 40% tin, the step comprising heating, in a non-oxidizing atmosphere at a temperature of about 950 to 1100 0., a substantially uniform mixture of particles of the above said low grade ore, an amount of a solid carbonaceous reducing agent corresponding to at least twice the tin-reducing equivalent of the tin content, with the production of carbon monoxide, of the ore, and from about 10% to 100% by weight of sulfur, based on the weight of the ore, for a time sufiicient to volatilize the resulting tin sulfide from the ore undergoing treatment.

2. In the method of recovering tin in the form of tin sulfide from a low grade, unreduced tin ore containing a substantial amount of metallic impurities and about 10% to tin, the step comprising heating, in a non-oxidizing atmosphere at a temperature of about 1020 to 1060 C., a substantially uniform mixture of particles of the above said low grade ore, an amount of a solid carbonaceous reducing agent corresponding to at least twice the tin-reducing equivalent of the tin content, with the production of carbon monoxide, of the ore, and from about 10% to by weight of sulfur, based on the weight of the ore, for a time suflicient to volatilize the resulting tin sulfide from the ore undergoing treatment.

t IRVING E. MUSKAT. ROBERT H. TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:'

UNITED STATES PATENTS Number Name Date 1,606,343 Burdick Nov. 9, 1926 1,847,991 Sulman et a1. Mar. 1, 1932 FOREIGN PATENTS Number Country Date 316,177 Great Britain Nov. 27, 1930 

1. IN THE METHOD OF RECOVERING TIN IN THE FORM OF TIN SULFIDE FROM A LOW GRADE, UNREDUCED TIN ORE CONTAINING A SUBSTANTIAL AMOUNT OF METALLIC IMPURITIES AND ABOUT 10% TO 40% TIN, THE STEP COMPRISING HEATING, IN A NON-OXIDIZING ATMOSPHERE AT A TEMPERATURE OF ABOUT 950* TO 1100* C., A SUBSTANTIALLY UNIFORM MIXTURE OF PARTICLES OF THE ABOVE SAID LOW GRADE ORE, AN AMOUNT OF A SOLID CARBONACEOUS REDUCING AGENT CORRESPONDING TO AT LEAST TWICE THE TIN-REDUCING EQUIVALENT OF THE TIN CONTENT, WITH THE PRODUCTION OF CARBON MONOXIDE, OF THE ORE, AND FROM ABOUT 10% TO, 100% BY WEIGHT OF SULFUR, BASED ON THE WEIGHT OF THE ORE, FOR A TIME SUFFICIENT TO VOLATILIZE THE RESULTING TIN SULFIDE FROM THE ORE UNDERGOING TREATMENT. 